1. Field of the Invention
The present invention relates generally to carbureted single-cylinder internal combustion engines, and more particularly to an intake manifold and intake port for same.
2. Description of the Related Art
In single cylinder air-cooled gasoline engines the induction system from the carburetor to the intake port of the cylinder head is often sized for minimum flow restriction and maximum induction flow area in order to obtain maximum power. This arrangement is satisfactory in achieving high power at wide open throttle. At lower speeds, however, the air stream within the induction system has a low velocity, is essentially streamlined, and lacks the turbulence necessary to keep the fuel in suspension. Under such low flow conditions a fluid stream of gasoline will tend to separate out and migrate along the walls of the induction system. This effect is most pronounced at elbow bends and at manifold joint sections where the manifold joins the carburetor and the cylinder head intake port. The gasoline which separates out tends to collect in puddles, especially where the geometry of the induction system involves arcuate sections and elbow bends. Such puddles can result in the feeding of nonhomogeneous nonstoichiometric mixtures to the combustion chamber even though the carburetor is maintaining a correct fuel/air mixture because the gasoline settles out within the induction system as the air flow decreases and is picked up again by the air stream as the air flow increases. Thus, the mixture alternates between being overly lean and overly rich. Consequently, on acceleration from idle, the fuel/air mixture introduced into the combustion chamber is extremely over-rich, causing the engine to emit black exhaust smoke, stumble, lag and sometimes stall.
It would be desireable to provide an induction system for small air-cooled internal combustion engines which maintains a homogeneous mixture of the fuel and air between the carburetor and the intake valve even at closed throttle conditions such as idle, while not unduly restricting flow at wide open throttle.